GLACIERS AND CLIMATE Mass balance ELA Pleistocene glaciation

GLACIERS AND CLIMATE • Mass balance • ELA • Pleistocene glaciation • Milankovic cycle • Albedo feedbacks Quelcaya ice cap, Peru

Geographical and Climatic conditions • high snowfall in winter • cool temperatures in summer • Moisture important!!! – Eg: Siberia and parts of Antarctica: low temperatures meet glacier growth requirements, but lack of adequate precipitation prevents glacier development

Annual Glacier Mass Balance • (Net)Accumulation zone = area where ice accumulates • (Net) Ablation zone= area where glacial ice melts • Equilibrium line where accumulation=ablation balance = 0 (at equilibrium)

Equilibrium Line Altitude

Where is the ELA?

Mass balance • NEGATIVE: glacier gets smaller • POSITIVE: glacier gets larger • ZERO MASS BALANCE: – no change in glacier size (mass, volume) – GLACIER STILL MOVING FORWARD!!!

ELA and climate • Positive Mass Balance -- ELA lower – Glacier gets larger • Negative Mass Balance -- ELA higher – Glacier gets smaller

How do glaciers reflect climate change? • Climate change: – changes in temperature – changes in amount of moisture – Glaciers sensitive to temperature fluctuations • climate change can cause glaciers to melt • but the relationship is not straightforward, – eg. Antarctica: climate change-->warmer-->more evaporation from ocean ->more water vapor -> more snowfall!

Ice ages • Ice ages return every 100, 000 years • approx. 20 ice ages • Pleistocene = most recent ice age, that started about 2 million years ago and ended ~10, 000 yrs ago • 4 major advances of ice, most recent ones: – Laurentide: ended 20, 000 yrs ago – Wisconsin: ended 100, 000 yrs ago – Presently we are in an interglacial period

Causes of ice ages? Milankovic cycles long term variations in Earth’s orbit around the Sun:

Glacial ages • During the last Ice Age, glaciers covered 32% of the total land area. • Little Ice Age: – 17 th century - late 19 th century – consistently cool temperatures – significant glacier advances.

Earth’s climate record

Glaciers sensitive to climate changes: a few facts • strong warming over the last 50 -200 yrs • increasing CO 2 levels • Alpine glaciers have been experiencing rapid retreat • Ice cap on Mt. Kilimanjaro has been decreasing by 82% in the last 88 years • Glaciers in the Alps decreased by 50% in volume

Ice-albedo (positive) feedback Global warming + + Glacial melt More energy absorbed + Decrease in surface of ice + Decrease in albedo +

Climatic responses- scenarios • winter temperature: – less, not more, snow – polar areas get little precip. (cold air) – if summer ablation same -- glacier retreats • summer temperature: – more cloud cover – less summer ablation – if winter accumulation same -- glacier grows

Climatic response (cont’d) • winter precipitation (snowfall) – if no change in temperature – some snow survives over summer – glacier advances – temperature crucial factor-

Glacier response -summary • Alpine glaciers and N. Hem. Ice caps expected to retreat under global warming scenario • NOTE: Antarctica expected to grow due to possible increase in humidity

Aster image, Patagonia, Chile

Indian Himalayas: Glacier ablation at Gangotri, source of the holy Ganges • glacier terminus retreated by 3 km ASTER Image courtesy of: NASA EROS Data Center, Sept. 9, 2001

Summary: GLACIERS AND CLIMATE • Mass balance • ELA • Pleistocene glaciation • Milankovic cycle • Albedo feedbacks Quelcaya ice cap, Peru